Enhanced read-ahead capability for storage devices

ABSTRACT

Enhanced read-ahead capabilities for storage devices are disclosed herein. In an implementation, data for a given write operation may be written to storage such that the location of the next write is stored with the data. Later, when the data is being read from storage, other data may be pre-fetched from the location of the next write that was written with the data. If the next location is the target of a subsequent read operation, the other data may be returned to the host immediately, since it will have already been read from the location where it was stored, thereby speeding-up the subsequent read operation.

TECHNICAL FIELD

Aspects of the disclosure are related to the field of storage devicesand, more particularly, to an enhanced read-ahead capability to improvethe speed of read operations.

BACKGROUND

As central processing units, graphics processors, and other processingelements have increased in speed, storage devices have become abottleneck in the overall performance of computing systems. The speed atwhich solid state drives (SSDs) operate relative to hard disk drives(HDDs) has mitigated this problem somewhat. Regardless, a given SSD canstill be a drag on a host and the performance of SSDs can vary greatlyfrom one to another.

The relative performance of a storage device may be evaluated based on anumber of factors, such as the capacity of a given device and its readand write speeds. While most write speeds have increased over time, readtime has been a critical limiting factor in the performance of storagedevices. Sequential read techniques have increased speeds to a certainextent, as have increased toggle rates—but at the expense of increasedpower consumption.

Random reads present a particular challenge to the goal of increasedspeed. In contrast with sequential reads, which allow large contiguousblocks of data to be read from adjacent locations on media, random readsseek data scattered across various non-adjacent locations on the media.Random reads thus introduce latency to the read process, which affectsthe overall performance of a storage device its associated host.

OVERVIEW

A read-ahead technique is disclosed herein to increase the speed atwhich storage devices read data. Data for a given write operation may bewritten to storage such that the location of the next write is storedwith the data. Later on, when the data is being read from storage, otherdata may be pre-fetched from the location of the next write that waswritten with the data. If the next location is the target of asubsequent read operation, the other data may be returned to the hostimmediately since it will have already been read from the location whereit was stored. This process thereby speeds-up the subsequent readoperation.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the disclosure may be better understood with referenceto the following drawings. The components in the drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the present disclosure. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views. While several embodiments are described inconnection with these drawings, the disclosure is not limited to theembodiments disclosed herein. On the contrary, the intent is to coverall alternatives, modifications, and equivalents.

FIG. 1 illustrates a computing system in an implementation.

FIG. 2 illustrates a write process in an implementation.

FIG. 3 illustrates a read process in an implementation.

FIG. 4 illustrates an operational scenario in an implementation.

FIG. 5 illustrates a computing system in an implementation.

FIG. 6 illustrates a write process in an implementation.

FIG. 7 illustrates a read process in an implementation.

FIG. 8 illustrates an operational architecture in an implementation.

FIGS. 9A-9B illustrate an operational architecture in an implementation.

FIG. 10 illustrates a power control process in an implementation.

DETAILED DESCRIPTION

An improved storage device is disclosed herein having enhancedread-ahead capabilities. In various implementations, read times aredecreased (and speed increased) by predicting which address will be readnext after a given read operation. The data at that address may bepre-fetched ahead of a subsequent read request targeting that address.

The predicted address may be derived from information saved about writecommands as they appear in the queue. Such address tracking may be usedduring the read of each address as a predictor to the next read command.In an example, the predicted address is obtained from the payload of thepreceding read operation. That is, during an earlier write operation,the address of the next write may be written to storage with the data inthe payload of a given write. Later, when that payload is the subject ofa read request, its payload may be parsed to obtain the address of whatwas the next write address. The next write address may then be utilizedas the next/predicted read address.

As such, the data at the predicted address may be pre-fetched ahead ofany subsequent reads that could potentially be directed to the sameaddress. The data may be buffered in anticipation of a relevant read. Ifthe next read request is directed to the predicted address, then thebuffered data may be returned immediately, without having to wait on aread operation. If the next read is not directed to the predictedaddress, the data may be discarded.

Obtaining the address of the next write command is possible because theprobability of having other write commands in the queue while performinga given write is high due to the amount of time it takes to program dataon media. Conversely, the probability of having other read requests inthe queue is low due to the relative speed of reads versus writes.Predicting this next read is therefore useful since it is likely duringa read that the read queue is empty.

In some implementations, power consumption may increase as a result ofthe enhanced read-ahead, since not all the predictions will besuccessful. A countermeasure to reduce redundant overhead andextra-power consumption is to track the success rate of the proposedpredictions described above. Predictive read may be conditionallyenabled when the success rate is above a certain threshold and disabledwhen it falls below the threshold.

In various implementations, the storage device may be, for example, asolid-state drive (SSD), a hard disk drive (HDD), a hybrid SSD-HDD, orany other type of storage device. The device includes a controller thatoversees how data is written-to and read-from media, such as NAND-basedflash memory, dynamic random-access memory (DRAM), magnetic datastorage, optical data storage, and/or any other type of storagetechnology.

The controller may be implemented in hardware, firmware, software, or acombination thereof, and bridges the memory components of the device toa host. In a hardware implementation, the controller includes controlcircuitry coupled to a storage medium. The control circuitry includes areceive circuit that receives write requests from a host. Each writerequest includes data that is the subject of the write request, as wellas a target address for the data. The target address may be a logicalblock address (LBA), physical block address (PBA), or other suchidentifier that describes where to store the data.

The control circuity also includes a location circuit that identifies anext write address for a next write request after the earlier writerequest. A write circuit in the control circuitry writes the data forthe write request and an indication of the next write address to thetarget address for the write request. In other words, the data that isthe subject of the write request is written to storage with the addressof the next write request. As used herein an “indication” refers to anydata value, bit, value, signal, flag, condition, offset, code, or numberthat identifies or may be used to ascertain the location of the set ofdata that will be subsequently stored on the media.

In a brief example, 4 bytes of a 16 kb page being written may be usedfor the address of the next write (0.025% overhead). The address of thenext write may be written in the header section of a given page,although it is also possible to store the address in the user-datasection of the page. Examples of the address include PBAs, LBAs, orboth, as well as any other information representative of the location ofthe next write. In some implementations, the next write address is theabsolute address of the location where the next data is stored,including die, page, and block information. In other implementations,the indication of the next write address may be an offset from thecurrent LBA or PBA that may be used to resolve the next address. Instill other examples, the next address may be written in a short-handversion of an address. The address of the next write may be stored in anencoded form, an unencoded form, or in any other manner.

Subsequent to the write requests, the host may communicate a readrequest that targets the same address as in the initial write request. Aread circuit in the control circuitry reads the data and the next writeaddress from the target address. In addition, the read circuitreads-ahead at a location indicated by the next write address to obtainnext data in advance of a next read request. As mentioned above, thenext write address—which serves as the read-ahead address—may beindicated by an LBA, a PBA, an offset, a flag, or the like. For example,in the case of an LBA, the control circuitry translates the LBA to a PBAin order to fetch the next data. In another example, no translation isneeded if the next write address was stored as a PBA. In the case of anoffset, signal, flag, or the like, the control circuitry may calculatethe read-ahead PBA from the present PBA and the value associated with anoffset, signal, flag or the like. Once the next read request iscommunicated by the host, the next data is ready to be returned to thehost immediately. In some cases, both the initial read request and thenext read request are considered random read requests, and the readoperations are therefore considered random reads. In someimplementations, the control circuitry further comprises a buffercircuit to store an indication of the next write address and to storethe next data. The indication of the next write address as-buffered maybe stored as a value that can be compared to the target address in arelation to subsequent read request. For example, the buffered value maybe an LBA, which can be compared against an LBA in a subsequent readrequest. In certain embodiments, if subsequent read requests utilizePBAs, then the buffered value may be PBA instead of an LBA. In somescenarios, addresses and data associated with multiple read-aheadoperations may be stored in the buffer simultaneously. The buffer may besized such that it can accommodate one or more pages of data. In onescenario, the buffer may be 96 kB or less of RAM, or the size ofapproximately four pages of data. However, it may be appreciated thatthe RAM size could increase, as could the page size.

A comparator portion of the control circuitry may then determine thatthe next target address specified in the next read request matches thenext write address. This may be accomplished by comparing the value ofthe next write address in the buffer with the value of the address inthe next read request. For instance, an LBA in the next read request maybe compared against an LBA in the buffer. In another example, a PBA inthe next read request may be compared against the PBA in the buffer. Insome alternative embodiments, the value stored in the buffer may differby an offset from the actual value of the next write address as storedon media or calculated during a read-ahead operation. In such asituation, the control circuitry would calculate the actual value beforecomparing it to the value in the next read request. The comparator orother element(s) of the control circuitry may responsively return thenext data to the host in reply to the next read request in a situationwhere the values match each other. The comparator may discard the nextdata if the next target address given in the next read request does notmatch the next write address.

The controller may include a write queue and a read queue in someimplementations. The read queue receives read requests from a host,while the write queue receives write requests. The read requests mayindicate where in non-volatile storage media to read data, therebyallowing the controller to fetch the data from the location indicated bya given read request.

Having done so, the controller parses a predicted address of a next readrequest from the payload read from the location. The controller may thenpre-fetch additional data from the predicted location of the next readrequest, ahead of actually receiving the next read request. If theactual location of the next read request differs from the predictedlocation, the controller may simply discard the next data and proceed toread from the actual location.

With respect to the write queue, each of the write requests in the queueindicate where to write the data for a given write request. A predictorportion of the controller identifies the predicted location for the nextread request based on the location indicated by a next write requestafter an earlier write request. A write portion of the controller maywrite, to the location indicated for the earlier write request, the datafor the earlier write request and an indication of the predictedlocation. A buffer portion of the controller may store the indication ofthe predicted location for the next read request and also the next data.

As mentioned above, a comparator portion may determine that the locationindicated by the next read request matches the predicted location forthe next read request. The comparator or other portion(s) of thecontroller may return the next data to the host. The next data may bediscarded if the location indicated by the next read request does notmatch the predicted location for the next read request.

Such enhanced read-ahead technology provides various technicaladvantages, as may be evident from the discussion above and thefollowing discussion of FIGS. 1-10. For example, pre-fetching data aheadof read request increases read speeds. This may be especially beneficialin the case of random reads, which take a longer amount of time tocomplete because their data are scattered about on the media. In anotherexample, the requesting application on the host need not be known to thecontroller. Rather, the controller may employ enhanced ahead with noknowledge of the requesting application.

Turning now to the drawings, FIG. 1 illustrates computing system 100 inan implementation of enhanced read-ahead technology. Computing system100 includes host 101 and storage device 110. Host 101 is representativeof any host sub-system that may write data to and read data from storagedevice 110. Storage device 110 is representative of any device capableof connecting to host 101 internally or externally for the purposes ofreading and writing data. Examples of storage device 110 include, butare not limited to, solid-state drives (SSDs), thumb drives, hard diskdrives (HDDs), hybrid SSD/HDD drives, and any variation or combinationthereof. Examples of computing system 100 include, but are not limitedto, personal computers, laptop computers, server computers, tabletcomputers, mobile phones, network drives, consumer electronics devices(e.g. cameras, televisions, and media players), gaming devices, durablegoods devices, and any other system, variation, or combination thereofthat utilize one or more storage devices.

Host 101 communicates with storage device 110 over connection 103.Connection 103 is representative of the one or more physicalinterconnects that couple host 101 and storage device 110 and over whichstorage communications may flow between the two. Host 101 may utilizeone or more interface protocols when communicating with storage device110, such as (but not limited to) Serial ATA (SATA), Fibre Channel,Firewire, Serial Attached Small Computer Systems Interface (SAS),Advanced Technology Attachment/Integrated Drive Electronics (ATA/IDE),Universal Serial Bus (USB), and Peripheral Component InterconnectExpress (PCIe).

Storage device 110 includes controller 111 and storage media 115.Controller 111 is representative of one or more processing elements thatperform a supervisory role over writing data to storage media 115 andreading data from storage media 115. Controller 111 is capable ofexecuting write process 200 and read process 300, described in moredetail in FIG. 2 and FIG. 3 respectively, which may be implemented inhardware, but also in firmware, software, or other forms of programinstructions executable by controller 111. Storage media 115 is anynon-volatile medium on which data may be written and read. Examplesinclude, but are not limited to, NAND flash media, DRAM media, phasechange media, magnetic media, and optical media. Connection 113 isrepresentative of the one or more physical interconnects that couplecontroller 111 and storage media 115.

In operation, host 101 communicates read and write requests tocontroller 111 to be carried out on storage media 115, of which writerequests 121 and read request 125 are representative. Controller 111executes write process 200 when handling write requests 121 and executesread process 300 when handling read request 125. The following is adetailed discussion of write process 200 and read process 300 and refersparenthetically to the steps in FIG. 2 and FIG. 3 respectively.

Referring to FIG. 2, controller 111 receives a given write request fromhost 101 (step 201). The write request includes that data to be writtenand a location indicative of where to write the data on storage media115. The location may be given by a physical block address (PBA), alogical block address (LBA), or any other suitable indication. In somecases, the location may not be given in the write request itself, butrather may be provided by host 101 separately or determined bycontroller 111 upon receiving the write request.

Next, controller 111 identifies the next location of the next writerequest submitted by host 101 (step 203). This may be accomplished by,for example, reading the address associated with the next write requestin the write queue. Controller 111 then generates a payload to bewritten to the location specified for the initial write request (step205). The payload may include at least the data for the first writerequest and the next location for the next write request. The nextlocation may be a PBA, but alternatively could be an LBA.

While only a single next location is included in the payload in thisexample, it should be appreciated that multiple locations could bestored in a single payload. For example, the next address and the nextaddress after that could both be stored in a given payload. In addition,while the term “next” as used herein refers to the very next address inthe queue, variations are possible. For example, the very next addresscould be skipped and the next after that used instead and included inthe payload.

Having generated the payload, controller 111 writes the payload to theinitial location specified for the write request (step 207). In thismanner, the data for the write request is stored with the identity ofthe location for the next write request in the queue. Write process 200may continue for subsequent write requests, writing the address of thenext write request to follow each preceding request with the data forthe request. The subsequent location information may serve as apredicted location for read process 300, a discussion of which followsbelow.

Referring to read process 300 in FIG. 3, controller 111 receives a givenread request from host 101 (step 301). The read request includes anaddress at which controller 111 is to read data. The location may bespecified as a PBA or an LBA, in which case controller 111 wouldtranslate the LBA into a PBA.

Controller 111 fetches the payload from storage media 115 at the addressgiven by the read request (step 303) and parses the payload into itsdata and the next location that was stored with the data in the contextof write process 200 (step 305). The data may be returned to host 101(step 306), while the next location is used to pre-fetch next data (step307).

It may be appreciated that the pre-fetch step need not always occur.Rather, controller 111 may refrain from attempting to pre-fetch data ifthe payload contains a null value or otherwise does not include a nextlocation. In another optional example, controller 111 may refrain fromthe parsing and prefetching steps if the read request is not a randomread request. That is, before proceeding to step 305 and step 307,controller 111 may first determine whether the read request is a randomread request. Controller 111 may ascertain itself that a read request isa random read or may be made aware of the fact by host 101.

The address of the next location and the data that is pre-fetched may bebuffered such that they are available when a subsequent read request isreceived. In some implementations, the payload may include more than onenext address, in which case the controller may pre-fetch and buffer datafrom multiple locations. Multiple “next addresses” would also then bebuffered.

Controller 111 may compare the address in the subsequent read request tothe next address in the buffer to determine if they are the same (or tomultiple next addresses if present in the buffer). If so, controller 111may return the pre-fetched data to host 101 in reply to the subsequentread request, rather than having to fetch it.

Referring back to the example scenario illustrated in FIG. 1, host 101submits write requests 121 to storage device 110. Write requests 121include a first request having data d1 and an address L1; the secondrequest includes data d2 and location L2; and the n^(th) requestincludes data do and location Ln.

Applying write process 200 to the first write request, controller 111generates payloads 123 to be written to storage media 115. Controller111 generates a payload d1_L2 from the data in the first request and theaddress in the second request. The payload is written to storage media115. Likewise, controller 111 generates a payload d2_L3 for the secondrequest. The payload generated for the n^(th) request includes the datafrom the n^(th) request and the location of the next write request inthe queue, or dn_Ln+.

Host 101 also submits read request, of which read request 125 isrepresentative. Read request 125 identifies location L1 as may berepresentative of, for example, a random read request, although othertypes of reads are possible.

Applying read process 300, controller 111 fetches (and pre-fetches)payloads 127 in response to read requests from host 101. For example,controller 111 fetches the payload from location L1, which is thepayload for the first write request discussed above, or d1_L2.

Controller 111 parses the payload to obtain the next location, L2. Thedata portion of the payload (d1) may be returned to host 101. Controller111 also pre-fetches the payload at location L2, in anticipation ofanother read request directed to L2. That payload is also parsed intoits data portion (d2) and location portion (L3).

Assuming that another read request is received that is directed to L2,controller 111 may immediately return a response with data d2, withouthaving to fetch the data. However, data d2 may be discarded oroverwritten after a period of time if no read requests are received thatare directed to L2. Controller may optionally pre-fetch the payload atlocation L3, and then again at location Ln+, and so on until aconstraint of limit is reached.

FIG. 4 illustrates an operational scenario 400 in an implementation thatdemonstrates various timing aspects of the enhanced read-aheadtechnology disclosed herein. Operational scenario 400 involves host 401,write queue 403, read queue 404, controller 405, and media 407. Whileshown separately, write queue 404 and read queue 404 may be implementedeither externally or internally with respect to controller 405. It maybe appreciated that other elements, connections, and the like may beinvolved but are not shown for purposes of clarity.

In operation, host 401 communicates two write requests to write queue403, denoted by w1 (d1,L1) and w2 (d2, L2). While shown as a directcommunication between host 401 and the queues, it may be appreciatedthat the requests may be routed through other physical or logicalelements before reaching write queue 403, including controller 405.

Controller 405 implements the write requests in the general order inwhich they are received in the queue. Therefore, controller 405implements w1 first, followed by w2. With respect to the first writerequest, controller 405 looks into the queue to identify the address ofthe next write request—that is, w2. With L2 known, controller 405generates a payload for w1, which includes d1 and L2. Controller 405then writes d1 and L2 to media 407 in the location specified by thefirst write request, L1.

In accordance with the general order of the queue, controller 405 nextprocesses the second write request. It is assumed for exemplary purposesthat a third write request is behind w2 in write queue 403 and isaddressed to L3. Controller 405 therefore generates a payload for w2that includes d2 and L3. The payload is then written to L2 in media 407.

Later, after the writes have been completed, host 401 may submit readrequests to obtain the data that was previously written for w1. Readqueue 404 is populated with the read request, which indicates theaddress at which to obtain the data. Controller 405 fetches the payloadstored at the indicated address, which includes data (d1) and a nextlocation (L2).

Controller 405 parses the payload into its data and location componentsand returns the data portion to host 401. With the location portion,controller 405 pre-fetches the payload at location L2. The payloadincludes data (d2) and another “next” location (L3). Controller 405buffers the data with the location from which it was retrieved (L2), asopposed to the location that was stored with the data. Controller 405could optionally perform another pre-fetch for the payload stored at L3.

Host 401 communicates a subsequent read request. Controller 405responsively compares the location in the subsequent read request to thelocation stored in the buffer. In this example, both addresses reflectL2. As such, controller 405 may reply to the read request with thebuffered data, d2, rather than having to fetch the data from media 407.

FIG. 5 illustrates computing system 500 in another implementation ofenhanced read-ahead technology as applied in the context of amulti-threaded environment. Computing system 500 includes host 501 andstorage device 510. Host 501 is representative of any multi-threadedsub-system that may write data to and read data from storage device 510.Storage device 510 is representative of any device capable of connectingto host 501 internally or externally for the purposes of reading andwriting data.

Thread 502 and thread 504 are each representative of the various threadsthat may be available in a multi-threaded environment. Each thread maybe assigned dynamically at run-time to a different application, utility,or component running in host 501. The threads submit read requests tostorage device 510, represented by requests 522 (associated with thread502) and requests 524 (associated with thread 504).

Host 501 communicates with storage device 510 over connection 503.Connection 503 is representative of the one or more physicalinterconnects that communicatively couple host 501 and storage device510. Host 501 may utilize one or more interface protocols whencommunicating with storage device 510, such as (but not limited to)Serial ATA (SATA), Fibre Channel, Firewire, Serial Attached SmallComputer Systems Interface (SAS), Advanced TechnologyAttachment/Integrated Drive Electronics (ATA/IDE), Universal Serial Bus(USB), and Peripheral Component Interconnect Express (PCIe).

Storage device 510 includes controller 511 and media 515. Controller 511is representative of one or more processing elements that control theread and write processes with respect to media 515. Controller 511 iscapable of executing write process 600 and read process 700, describedin more detail in FIG. 6 and FIG. 7 respectively. Media 515 is anynon-volatile medium on which data may be written and read. Examplesinclude, but are not limited to, NAND flash media, DRAM media, phasechange media, magnetic media, and optical media. Connection 513 isrepresentative of the one or more interconnects that couple controller511 and media 515.

In operation, host 501 communicates read and write requests tocontroller 511. Controller 511 executes write process 600 when handlingwrite requests and read process 700 when handling read requests. Thefollowing is a detailed discussion of write process 600 and read process600 and refers parenthetically to the steps in FIG. 6 and FIG. 7respectively.

Referring to FIG. 6, controller 511 receives multiple write request2from host 501 (step 501). Each write request includes the data to bewritten and a location indicative of where to write the data on media515. The location may be given by a physical block address (PBA), alogical block address (LBA), or any other suitable address. In somecases, the location may not be given in the write request itself, butrather may be provided by host 501 separately or determined bycontroller 511 upon receiving the write request.

For any given write request, controller 511 identifies the threadassociated with the next request after it (step 603). The thread may beidentified in the next write request or may be determined in some othermanner. Controller 511 compares the thread associated with the instantrequest to the thread associated with the next request to determine ifthey are the same (step 605).

If the threads are the same, then controller 511 generates a payloadcomprised of the data for the instant request and the next address ofthe next write request (step 607). The payload is then written to theindicated address (step 609). However, if the threads are not the same,then controller 511 simply writes the data to the indicated address(step 606), thereby conserving resources by avoiding the step ofgenerating a payload.

Referring to FIG. 7, controller 511 receives a read request thatidentifies a target address (step 701). Controller 511 responsivelychecks a read-ahead flag to determine whether any information had beenbuffered for a previous read request (step 703). If the flag is enabled,controller 511 evaluates the target address in the request against theaddress stored in the buffer (step 705). If they are the same, thencontroller may read data from the buffer that was pre-fetched in thecontext of handling a previous read request (step 706).

If the addresses are not the same, then controller 511 proceeds to fetchthe payload at the specified address in the read request (step 707).Controller 511 parses the payload into its component parts, whichinclude at least data and an address pertaining to the next data to bewritten after the subject data (step 709).

With the data in-hand, controller 511 may read out the data to host 501(step 710). Controller 511 also checks if the next address is null orsome other value that indicates that a next address was not written tostorage (step 711). This may be the case when, for example, the nextwrite request to follow a given write request did not originate from thesame thread (see step 605 above with respect to FIG. 6).

If the next address value is null, the controller 511 sets the flag todisabled (step 712) so that, upon receiving a subsequent read request,the step of comparing addresses may be skipped. If the next address isnot null, controller 511 sets (or maintains) the flag value to enabled,so that target addresses in a subsequent read request may be compared(step 713).

Having set the flag, controller 511 pre-fetches the payload stored atthe location of the next address parsed from the subject payload (step715). Controller 511 stores the next data from the pre-fetched payloadin a buffer (step 717), along with the address corresponding to the nextdata. That next address may be compared to a subsequent target addressincluded in a subsequent read request when read process 700 returns tostep 705.

FIG. 8 illustrates an operational architecture 800 in an implementationof the write-side of enhanced read-ahead technology and an associatedexample scenario. In relation to FIG. 8, FIG. 9A and FIG. 9B illustratean operational architecture 900 in an implementation of the read-side ofsaid enhanced read-head technology, as well as an associated examplescenario. It may be appreciated that the two architectures could becombined (without any redundant elements) in the context of a suitablestorage device, such as an SSD, hybrid HDD/SSD, or the like.

Referring to FIG. 8, operational architecture 800 includes a write queue810, media 810, and various operational modules represented by locatemodule 801, receive module 803, and write module 805. Locate module 801,receive module 803, and write module may be implemented in hardware,firmware, or other software, as well as any variation or combinationthereof. Write queue 810 may be implemented externally from media 830but could also be implemented internally. In either case, write queue810 is accessible to one or more of locate module 801, receive module803 and write module 805. It may be appreciated that operationalarchitecture 800 may include other elements that are omitted for thesake of clarity, such as a system bus, interfaces and interconnections,and the like.

In operation write requests are received into write queue 810 from ahost (not shown) and occupy an order or place in the queue. The writerequests are represented by request w1 in place 811; request w2 in place813; request w3 in place 815, and request n in place 817. Accordingly,the write requests are handled in that order: w1, w2, w3, wn, and so on.

Receive module 803 receives the write requests as they are dispatchedfrom write queue 810 to be executed. As an example, receive module 803receives request w1 and passes it to write module 805. Request w1includes data (d1) and a location identifier (L1) of where to write thedata.

Locate module 801 looks into write queue 810 to identify the location ofthe next write request in the queue after the subject write request,which in this case is w2. The location of w2 is L2, and so locationmodule 801 passes L2 to write module 805. Write module 805 receives boththe information from receive module 803 and the information from locatemodule and generates a payload to be written to L1. In this example, thepayload 831 is a combination of d1 and L2.

Similar operations are carried out with respect to the other writerequests in the queue. Payload 833 is generated in association with w2and includes data d2 and location L3. Payload 835 is generated inassociation with w3 and includes data d3 and location L4. Finally,payload 837 is generated in association with wn and includes data do andlocation Ln+. In this manner, the payloads may be examined during theread process and pre-fetched if appropriate, thereby speeding up theread process.

Referring to FIG. 9A, operational architecture 900 includes a read queue950, media 910, and various operational modules represented by comparemodule 941, read module 943, and buffer 947. Read module 943 may includeparse module 945, although it may be implemented externally with respectto read module 943. Compare module 941, read module 943, buffer 947, andparse module 945 may be implemented in hardware, firmware, or othersoftware, as well as any variation or combination thereof. Read queue910 may be implemented externally from media 930 but could also beimplemented internally. In either case, read queue 910 is accessible toone or more of compare module 941, read module 943, and buffer 947. Itmay be appreciated that operational architecture 900 may include otherelements that are omitted for the sake of clarity, such as a system bus,interfaces and interconnections, and the like.

In operation, read requests are received into read queue 950 from ahost. The read request are represented by r1 in FIG. 9A, and r2 and r3in FIG. 9B. The requests have an order or place in the queue,represented by place 951, place 953, and place 955 respectively. Theread requests are assumed for the sake of illustration to be random readrequests, as opposed to sequential read requests, although sequentialread requests could be interspersed among the random read requests.

The read requests are taken of the queue and communicated to comparemodule 941. Compare module 941 compares the address in a given readrequest to an address that is buffered in buffer 947 (if any) todetermine if the subject data needs to be fetched or has already beenpre-fetched. In this example, read request r1 relates to location L1. L1is compared to Lx in buffer 947. Since they do no match, compare module941 passes the address to read module 943.

Read module 943 responsible fetches payload 931 from location L1. Parsemodule 945 parses the payload into its component parts, d1 and L2. Readmodule 943 is able to return d1 to the host and pre-fetches payload 933from L2. Payload 933 includes data d2 and location L3. Data d2 iscommunicated to buffer 947 to be stored in association with location L2.

FIG. 9B illustrates a continuation of the example scenario begun in FIG.9A. In FIG. 9B, read request r2 is received and taken off the queue bycompare module 941. Here, compare module 941 determines that the targetaddress in r2 is the same as the stored address in buffer 947.Accordingly, compare module 941 instructs read module 943 to read outdata d2 from buffer 942 to the host. Read module 943 could be omitted inthis step.

Since the payload at location L2 referenced a next address of L3, readmodule could optionally pre-fetch payload 935 at L3. In so doing, parsemodule would parse payload 935 to obtain data d3. Data d3 and locationL3 would be stored in buffer 947 to be compared against one or moresubsequent read requests.

FIG. 10 illustrates a power control process 1000 in an implementationwhereby the enhanced read-ahead technology disclosed here is dynamicallyenabled and disabled based on various operating conditions. A controllerin a solid-state drive or other suitable storage device may employ powercontrol process 1000, which may be implemented in hardware, firmware, orother software.

In operation, a given controller tracks the hit rate for read-aheadattempts that are made in the context of an enhanced read process (step1001). The hit rate may pertain to the rate at which data that ispre-fetched is actually requested by a subsequent read request. Forinstance, an initial read request directed to a first location mayresult in a payload that identifies a second location. The data at thesecond location would then be pre-fetched ahead of any subsequent readrequest that may (or may not) target the second location. If the nextread request is directed to the second location, then the pre-fetchwould be considered a hit, whereas if the next read request is directedto a different location, the pre-fetch would be considered a miss.

The controller may track the success rate of the pre-fetch operations bycounting how many times pre-fetched data becomes the subject of asubsequent read request. The controller may also analyze whether or notthe hit rate falls below a given threshold (step 1003).

If the hit rate remains at or above the threshold, then the controllermay continue to operate with the read-ahead process enabled. If the hitrate falls below the threshold, the controller disables the read-aheadprocess (step 1005).

To re-enable the read-ahead process, the controller periodicallyevaluates one or more other conditions (step 1006). For example, theread-ahead may be disabled for a period of time, at the expiration ofwhich it is automatically re-enabled. In another example, the read-aheadmay remain disabled until a battery level or other power condition ismet. Until then, the controller operates with the read-ahead processdisabled.

Disabling the read-ahead process may conserve power, processing cycles,or other resources in the face of a high rate of missed read-aheadattempts. Re-enabling the process upon a change in conditions allows thedevice to regain the advantages of enhanced read-ahead.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or computer programproduct. Accordingly, aspects of the present invention may take the formof an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.) or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module” or “system.”Furthermore, aspects of the present invention may take the form of acomputer program product embodied in one or more computer readablemedium(s) having computer readable program code embodied thereon.

The included descriptions and figures depict specific embodiments toteach those skilled in the art how to make and use the best mode. Forthe purpose of teaching inventive principles, some conventional aspectshave been simplified or omitted. Those skilled in the art willappreciate variations from these embodiments that fall within the scopeof the disclosure. Those skilled in the art will also appreciate thatthe features described above may be combined in various ways to formmultiple embodiments. As a result, the invention is not limited to thespecific embodiments described above, but only by the claims and theirequivalents.

What is claimed is:
 1. An apparatus comprising: a storage medium; andcontrol circuitry coupled to the storage medium and comprising: areceive circuit configured to receive a write request from a host, thewrite request comprising data and a target address for the data; alocation circuit configured to identify a next write address for a nextwrite request; and a write circuit configured to write to the targetaddress the data of the write request and an indication of the nextwrite address.
 2. The apparatus of claim 1 wherein the control circuitryfurther comprises a read circuit configured to: read the data and theindication of the next write address from the target address in responseto a read request; and read next data from the next write address inadvance of a next read request.
 3. The apparatus of claim 2 wherein thecontrol circuitry further comprises a buffer circuit to store theindication of the next write address and to store the next data.
 4. Theapparatus of claim 3 wherein the control circuitry further comprises acomparator configured to determine that a target address specified inthe next read request matches the next write address and to coordinatewith the control circuitry to return the next data in reply to the nextread request.
 5. An apparatus comprising: non-volatile storage media;and control circuitry coupled to the non-volatile storage media andcomprising: a read queue configured to receive read requests from ahost, wherein each of the read requests indicate where in thenon-volatile storage media to read data; and a read circuit configuredto: fetch the data from a location indicated by a read request; parse,from the location indicated by the read request, a predicted address ofa next read request; and pre-fetch additional data from the predictedlocation of the next read request.
 6. The apparatus of claim 5 whereinthe control circuitry further comprises: a write queue to receive writerequests from the host, wherein each of the write requests indicatewhere to write the data for a given write request; a predictor portionto identify the predicted location for the next read request based onthe location indicated by a next write request after an earlier writerequest; and a write portion to write, to the location indicated for theearlier write request, the data for the earlier write request and anindication of the predicted location.
 7. The apparatus of claim 6wherein the control circuitry further comprises a buffer to store theindication of the predicted location for the next read request and tostore the next data, wherein the buffer comprises random access memory(RAM) having a size that accommodates no more than four pages of data.8. The apparatus of claim 7 wherein the control circuitry furthercomprises a comparator portion to determine that the location indicatedby the next read request matches the predicted location for the nextread request and to responsively return the next data.
 9. The apparatusof claim 7 wherein the control circuitry further comprises a comparatorportion to determine that the location indicated by the next readrequest does not match the predicted location for the next read requestand to responsively discard the next data, and wherein the read requestscomprise random read requests.
 10. A storage device comprising:non-volatile storage media; a controller coupled with the non-volatilestorage media and configured to: maintain a queue of write requests,wherein each of the write requests includes data and a specifies wherein the non-volatile storage media to write the data; generate a payloadfor each of the write requests, wherein the payload comprises the datafor a given write request and a next location for a next write requestreceived after the given write request; and write the payload for eachof the write requests to the location in the non-volatile storage mediaspecified for each of the write requests.
 11. The storage device ofclaim 10 wherein the controller is further configured to maintain aqueue of read requests and, for a given read request in the queue ofread request, predict the location for the given read request based onthe indication of the next location in the payload obtained for aprevious read request.
 12. The storage device of claim 11 wherein thecontroller is further configured to read a next payload from the nextlocation before receiving the given read request, store next data fromthe next payload in a buffer, and store the indication for the nextlocation in the buffer.
 13. The storage device of claim 12 wherein thecontroller is further configured to compare the indication for the nextlocation to an actual location specified by the given read request anduse the next data in the buffer when the next location matches theactual location.
 14. The storage device of claim 12 wherein thecontroller is further configured to compare the indication for the nextlocation to an actual location specified by the given read request anddiscard the next data in the buffer when the next location does notmatch the actual location, wherein the read requests comprise randomread requests and wherein the payload further comprises a subsequentlocation for a subsequent write request received after the given writerequest.
 15. A method comprising: maintaining a queue of write requestsfrom a host, wherein each of the write requests includes data and aspecifies where in non-volatile storage media to write the data; foreach of the write requests, determining whether a source of a subsequentwrite request in the queue is the same as the source of a given writerequest; writing a payload for each of the write requests to thelocation in the non-volatile storage media specified for each of thewrite requests, wherein the payload comprises the data for the givenwrite request and the payload further comprises, if the source is thesame for the subsequent write request as for the write request, anindication of a next location for a next write request positioned in thequeue after the given write request; receiving read requests from thehost; and for a given read request, predicting the location for thegiven read request based on the indication of the next location in thepayload obtained for a previous read request.
 16. The method of claim 15further comprising: reading a next payload from the next location beforereceiving the given read request; storing next data from the nextpayload in a buffer; and storing the indication for the next location inthe buffer.
 17. The method of claim 16 further comprising comparing theindication for the next location to an actual location specified by thegiven read request, and using the next data in the buffer when the nextlocation matches the actual location.
 18. The method of claim 15 whereinthe read requests comprise random read requests, wherein the source ofthe subsequent write request comprises an application thread in amulti-threaded environment.
 19. A system comprising: means for receivingread requests from a host, wherein each of the read requests indicateswhere in a non-volatile storage medium to read data; means for readingthe data from a location specified by a read request; means for reading,from the location specified by the read request, a predicted location ofa next read request; and means for reading additional data from thepredicted location of the next read request.
 20. The system of claim 19further comprising: means for maintaining a write queue of writerequests received from the host, wherein each of the write requestsspecifies where to write the data for a given write request; means fordetermining the predicted location for the next read request based onthe location specified by a next write request positioned in the queueafter an earlier write request; and means for writing, to the locationspecified for the earlier write request, the data for the earlier writerequest and an indication of the predicted location for the next readrequest.